Vulnerability and Risk Assessment (VRA) for Landslide and Flood of Sibutad Municipality, Zamboanga del Norte

By El-Jedidiah O. Villacampa

SIBUTAD, Zamboanga del Norte – A risk exposure analysis has been conducted in Sibutad Municipality, Zamboanga del Norte in July 2016 and was headed by El-Jedidiah O. Villacampa (Senior Geologist), accompanied by geologists namely Kris Elvis N. Alferez, Daryl Mae M. Gerodiaz, Ian T. Demetillo and Nysie D. Agbayani. This analysis is made by associating the identified landslide and flood geohazards with the three elements such as population, road and infrastructure based on the published MGB Geohazard Map for Sibutad as well as the GIS software application. The exposure of each element is expressed in the form of percentage from total quantity and is assessed separately according to the four categories of landslide and flooding namely high – very high, moderate and low.

Sibutad Municipality is located at the northeastern coast of the Zamboanga Peninsula. It is bounded to the west and south by Dapitan City, to the north by the Murcielagos Bay and to the east by Rizal Municipality. It is subdivided into sixteen (16) barangays namely, Minlasag, Sipaloc, Dalepa Marapong, Bagacay, Poblacion, Calilic, Sibuloc, Kanim, Maysaysay, Libay, Calube, Panganuran, Sinipay, Sawang, and Oyan. It is approximately centered at geographic coordinate’s 08°36′ 51.6” North latitude and 123°28′ 43.9” East longitude (Sibutad Municipal Hall). It is accessible from any point in Zamboanga del Norte Province or Zamboanga Peninsula through the coastal national road and through a provincial road.

The topography of Sibutad Municipality is a valley that is bounded by a north-south trending steep ridge to the west and by a northwest-southeast ridge to the northeast. Its central to southern areas are situated in the valley that is characterized by a generally rolling terrain. The valley has a network of creek/river channels that serve as headwater tributaries of Poro River. Having such condition flooding is generally are more common than landslide as hazard. The coastal portions in the north have narrow low-lying areas bounded closely by steep ridges. Thus, the coastal areas in the north are more susceptible to landslide rather than flooding. Those areas along the ridges or along their slopes are naturally more susceptible to landslide.

The exposures of the sixteen (16) barangays of Sibutad Municipality to landslide and flood hazards have been analyzed by associating each hazard to every element at risk such as population, roads and infrastructure imprints. In terms of its population exposure to landslide, there are ten (10) barangays having portions under high to very high susceptibility, twelve (12) barangays with portions under moderate susceptibility, and twelve (12) barangays with portions under low susceptibility. For the population exposure to flooding, there are nine (9) barangays having portions under high susceptibility, and ten (10) barangays with portions under moderate to low susceptibility.

In terms of its road exposure to landslide, there are six (6) barangays having portions under high susceptibility, ten (10) barangays having portions under moderate susceptibility, and eleven (11) barangays having portions under low susceptibility. For the road exposure to flooding, there are ten (10) barangays with portions under high susceptibility; and seven (7) barangays with portions under moderate to low susceptibility.

In terms of its infrastructure exposure to landslide, there are ten (10) barangays having portions under high susceptibility, twelve (12) barangays with portions under moderate susceptibility, and twelve (12) barangays having portions under low susceptibility. For the infrastructure exposure to flooding, there are nine (9) barangays with portions under high susceptibility, and eleven (11) barangays with portions under moderate to low susceptibility.

Figure 1. Partly flooded barangay hall of Panganuran (left). Tilted post along Panganuran-Kanim road which is an indication of slope failure.

Figure 2. Population exposure to High – Very high landslide susceptibility: Percentages of the local barangay population exposed to the High – Very high landslide susceptibility rating show barangays Magsaysay, Libay, Panganuran, Kanim and Sawang to have the most exposure.

Figure 3. Population exposure to High flood susceptibility: Percentages of the local barangay population exposed to the High flood susceptibility rating show Barangay Marapong as the most exposed, followed by barangays Oyan, Sawang, Kanim, Libay and Calube.

Figure 4. Road exposure to High – Very high landslide susceptibility: Percentages of the Road Length exposed to the High to Very high landslide susceptibility rating shows barangays Calube and Panganuran having more than 70% exposure to such hazard category; at a lesser degree are Libay, Sawang, Kanim and Magsaysay with about 10-30% exposure.

Figure 5. Road exposure to High flood susceptibility: Percentages of the Road Length exposed to the High Flood susceptibility rating shows about 20% exposure for Barangay Magsaysay; at a lesser degree are barangays Minlasag, Poblacion Sibuloc, Sipaloc, Calilic and Calube with about 2-5% exposure.

Figure 6. Infrastructure exposure to High – Very high landslide susceptibility: Percentages of the Infrastructures exposed to the High to Very Landslide susceptibility rating shows 25% exposure for Barangay Calube; followed by barangays Panganuran with 41%, Sawang with 30% and Libay with 20% exposure.

Figure 7. Infrastructure exposure to High flood susceptibility: Percentages of the Infrastructures exposed to the High Flood susceptibility rating shows 38% exposure for Barangay Kanim, followed Panganuran with 20%, and Marapong with 15%.

(This excerpt was taken from the MGB-IX Technical Report entitled “Vulnerability and Risk Assessment (VRA) for Landslide and Flood of Sibutad Municipality, Zamboanga del Norte”.)

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